Steam stirred homogeneous nuclear reactor



June 3, 1958 H. M. BUSEY I 2,837,476

STEAM STIRRED HOMOGENEOUS'NUCLEAR REACTOR Filed Jan. 27, 1956 V 2 Sheets-Sheet 1 W/ TNESSES F /'g JNVEN TOR. v

w Harold M Busey June-3, 1958 H. M. BUSEY STEAM STIRRE'D HOMOGENEOUS NUCLEAR REACTOR Filed Jan. 27, 1956 2 Shets-Sheet 2 M II' Fig 2 IN V EN TOR. Harold M Busey STEAM STIRRED HOMOGENEOUS NUCLEAR REACTOR Harold M. Busey, Los Alamos, N. Mex., assignor to the United States of America as represented by the United States Atomic Energy Commission Application January 27, 1956, Serial No. 561,961

5 Claims. (Cl. 204--193.2)

The present invention relates to nuclear reactors and more particularly to homogeneous nuclear reactors utilizing a liquid fuel.

The nuclear reactor of the present invention is an improved reactor of the homogeneous type, and is described as particularly suitable for use as a research de vice where a maintenance free reactor of moderately high neutron flux is desired.

Homogeneous reactors of the priorartgenerally require extensive fuel handling and gas recombining systems; Also, in the prior art reactors, extensive fuel circulating apparatus is required or such reactors are drastically restricted to low power levels because of reliance on convection circulation. No such restrictions are required in the present invention, since convection" circulation is materially aided by the design and operating temperature of the system.

Although the description of the preferred embodiment is specific to a power level of the order of 100 kilowatts at which the central neutron flux is about neutrons per square cm. per sec. using ordinary water as a moderator, an appropriate scale-up of the reactor ofthe'present invention could operate in the megawatt region for heat or power generation. The modifications required would include a larger critical region, heat capacity, and volume of fuel.

The preferred embodiment of the present invention provides for the removal of heat from the critical region by utilizing the steam bubbles formed in the critical region. extending small diameter tubes. The liquid fuel is directed up these tubes and down the adjacent annular area containing heat exchanging apparatus and back into the critical region. It is the relation of the length and diameter of these tubes which distinguishes the present invention from the circulating systems of the prior art.

Further, in the present invention the liquid-gas;inter; face is not within the critical region, i. e. not within the geometry which determines the critical mass. Therefore, disturbances on the liquid surface will have a reduced effect upon the power and neutron level.

exchanging The critical region has a plurality of upwardly present invention showing the internal components thereof ahom'ogeneous reactor in a simple and rapid manner without the use of complicated circulating apparatus.

A still further obect of the present invention is to provide a method and apparatus for circulating the liquid fuel of a homogeneous reactor which results in a highly stable neutron flux level,

Other objects and advantages of the present invention will'become more apparent from the following descrip tion including drawings, hereby made fication, wherein: p

Figure 1 is a sectional view of one embodiment of the a part of the speci- Figure 2 shell and associated circulating tubes,

Figure 3 is a schematic diagram of the circulating system, and

Figure 4 is a schematic diagram of one modification of the present invention.

APPARATUS The preferred embodiment of the present invention shownfin Figure 1 comprises a closed reactor vessel 11,

preferably fabricated from stainless steel, having a The reactor of the present inventionis primarily controlled by its negative temperature coeflicient of'reactivity and the power level may be adjusted by regulating the flow of cooling fluid. For a steady neutron flux, a constant rate of flow will be required. However, conventional control rods may be used if desired.

Therefore, it is an object of the present invention to provide a homogeneous nuclear reactor which is relatively a method and apparatus for circulating the. liquid f uel flanged top plate asembly'12. The top plate assembly 12 consists of the vessel flange, a central plate 13 and a manifold plate 13a. The central plate 13 is sealed to the flange of the reactor vessel 11 and contains appropriate coolant inlet channels and steam outlet channels connected, respectively, to a coolant supply and power producing facilities. top of central plate 13.

The interior chamber of the vessel 11 of the preferred embodiment may be divided into three sections. first section is the critical region and is located near the bottom of the vessel 11. The second region is the heat exchanger and tube bundle region 15, and is located immediately above the critical region. The third region is the gas recombination region 16 ,Whichis located in the top of the vessel 11, i. e., above region 15. The critical region 14 of the vessel 11 in the preferred embodiment has a spherical reaction shell or baflle 17 fabrication from stainless steel having a thickness of about 0.1 inch. In this manner its effect upon critical dimension calculations is negligible. The lower portion of the reaction shell 17 is perforated as at 18 or otherwise partially openso thatliquid fuel may enter. action shell 17 is supported in any conventional manner in spaced relation to the bottom and the sides of vessel 11 thereby allowing liquid fuel to flow through the channel 19 so formed. Channel 19 has approximately the same cross sectional flow area as the total flow area of the tubes 20. p

Extending upwardly from the critical region is a bundle of small diameter tubes 20 Welded to the top portion of reaction shell 17. These tubes extend upwardly from the reaction shell 17 and connect the interior of the shell 17 with the upper portion of the heat exchanger region 15.; The'tubes 20 are spaced from the walls of vessel 11 thereby forming down-channel 21. The number of tubes required is dependent upon the circulation rate required. For example, in the specific embodiment being described about of these tubes would be required for the desired power output and circulation rate.

The tubes are welded or otherwise attached to each other in such a manner that the interstices between tubes are sealed from the liquid fuel. The length and diameter of :theflctitigal region 17, so that the majority of the'bubbles Patented June 3,

is a detailed sectional view of the reaction 1 The manifold 13a is sealed to the The i The re are formed in the tube rather than in the critical region. The diameter of the tube should be of the same order of magnitude as the diameter of the bubble upon reaching the upper portion of the tube. These relations result in a greater circulation rate than is possible by utilizing a single tube. The reason for the increased rate of circulation with a plurality of tubes is that the small diameter of the tubes approximates to a closer degree the average size of the bubble formed, so that a geyser effect takes place in each tube forcing the liquid fuel out the top of the tube as the bubble rises. Furthermore, with a plurality of tubes, bubble surges are random and have very little effect on the reactivity. With a single channel the presence of a series of bubbles produces a surge in circulation, and allows neutrons to escape more easily from the critical region, since the reflective influence of the bubbles is considerably lower than that of the liquid.

The length of the tubes is also important. The bubbles are originally formed as microscopic bubbles in the reaction shell 17. As these bubbles rise in the tubes, they coalesce to larger bubbles. The tubes must be long enough so that sufiicient time is available for this coalescence to become appreciable in order that the geyser effect will function to circulate the liquid fuel. It has been found that optimum circulation is obtained, at an operating temperature of 100 C., if the tubes are at least as long as the height of the reaction region, although no appreciable adverse effect was found by reducing the length the order of a few centimeters less than the reaction regions height.

The diameter of the tubes has been found to be critical if maximum circulation is desired. For the specific instance of spherical reaction shell of about 25 cm. diameter, a tube length of about 25 cm. and an operating temperature of 100 C., the tube diameter which gives maximum efficiency in circulating the liquid fuel is about 1 cm. Further it has been found that this diameter is not dependent upon the diameter of the critical region.

If the diameter of the tubes in the particular embodiment being described is increased to greater than about 15 mm., or is reduced to less than about 8 mm., it has been found that an undesired effect on the circulation rate results. The tubes 20 are preferably thin walled stainless steel tubes of approximately equal length. In the preferred embodiment shown in Figure 1 no provision has been made for a central control rod. However, if such a rod isdesired, several of the centrally located tubes may be removed and a sleeve (not shown) for the control rod inserted. Such a sleeve would extend upwardly through the gas recombining region and top plate assembly.

The heat exchanger 22 consists of a series of fiat spaced coils of X inch 0. D., A; inch I. D. stainless steel tubing, the tube bundle having a generally cylindrical form. The heat exchanger 22 is manifolded in flange 13a, and is connected to annular coolant channels 23 and 24. The heat exchanger inlet and outlet pipes 25 are evenly distributed around the interior surface of the vessel 11, only two being shown for illustration purposes. Coolant inlet 26 and coolant outlet 27 are connected, respectively, to annular inlet channel 23 and annular outlet channel 24, which are located in the bottom surface of manifold plate 13a. The heat exchanger 22 is supported by the outlet and inlet pipes 25 which are attached to the top plate assembly 12, so that the entire fuel cooling apparatus may be removed with the top plate assembly 12.

Above the upper extremity of the heat exchanger 22 is a series of fine mesh screen baffles 28 for preventing splashing of the liquid fuel upwardly into the recombining region, and to act as an entrainment trap for 4 droplets of fuel forced upwardly by the geyser action in the tubes 20.

The level 29 of the liquid fuel during operation is approximately equal to or slightly below the upper extremity of tubes. 20. The heat exchanger area located above the liquid level 29 functions to condense the steam and return it to the liquid fuel.

A liquid fuel inlet pipe 30 is provided which is sealed to the top plate assembly 12 and extends to the bottom of the interior of reactor 11. Through this inlet pipe, the liquid fuel is introduced into the reactor. The inlet pipe is connected through a control system (not shown) to a storage tank (not shown). Thus the fuel may be removed from the reactor and stored at a remote, shielded location, if maintenance of the reactor components is required. Inlet pipe 30 also provides a means for adding fissionable material, moderator, or other material to the liquid fuel, as this may be required after operating the reactor for some time.

The recombiner region, indicated generally at 31 and supported by bracket 32, and its arrangement is described in copending application Serial No. 493,579 by Harold M. Busey, filed March 10,- 1955, entitled Method and Apparatus for Catalytically Combining Gases, the subject matter of which is incorporated herein by reference.

The reflector, shielding and thermal column construction and control apparatus are also not descirbed herein, since the size and type of such components are well known in the art.

The upper portion of the reactor vessel 11 may be enclosed in a coolant jacket, not shown, to aid the convection circulation in the gas recombining region and the cold leg of the fuel circulating region.

Between the vessel 11 and the reflector 33, a sleeve 34 is located which is fabricated from a neutron absorbing material, such as cadmium, boron or similar material. The sleeve 34 is movable parallel to the axis of the vessel 11 by manual or automatic means (not shown) and is preferably supported by an electromagnet 35. In this manner the operation of the reactor can be controlled by merely de-energizing the electromagnet 35 which will allow the sleeve 34 to fall to its bottom position thereby surrounding the critical region 14 and cutting off reflected neutrons.

Critical region and fuels Various liquid fuels such as, for example, solutions or slurries, may be used in the reactor of the present invention. These include, but are not limited to, enriched uranyl nitrate or uranyl sulphate in ordinary or heavy water, as well as liquid fuels including plutonium as the fissionable material. Only one specific example will be given, although no limitation is thereby intended.

A solution of enriched uranyl sulfate (UO SO in ordinary water having, for example, of the order of 0.5 molar solution, is thepreferred fuel concentration for the reactor of the present invention. This type of liquid fuel has been used in homogeneous reactors in the past and many of its characteristics are known. (See An enriched homogeneous nuclear reactor, Review of Scientific Instruments, volume 22, No. 7, pages 489-499, July 1951, and AECD-3287, Technical Information Service, Oak Ridge, Tennessee, 1952.)

The fissionable component of the preferred fuel is uranium enriched in the isotope U to a value of about percent. The reflector material may be of a material well known in the art as a neutron reflector, such as graphite.

The configuration of the critical region is as a close approximation one-half cylindrical and one-half spherical.

Thus the critical size is determined by extrapolating between the critical size for a sphere and the critical size for a cylinder. Each of these calculations, as well as the extrapolation are well known in the art. Such calculations are performed in accordance with the generally accepted theory asdescribed 'in Glasstone and Edlund,"-

The Elements Lofl Nuclear Reactor VIII (Van Nostrand' Co., l952)."

By this analysis the approximate quantities andprop Theoryjf chapter tions for the preferred liquid fuel :ar'ejas follov'v's:

eter plus a cylinder 125 cm. d ameter f;

I 2 m fh l Moderator Normal water 15 .litersl Reflector Graphite (60-inch cube) Utilizing this fuel solution the power output would approximate 1070 kw. .wi'thf at-maximum thermal .flux of the; order of 10 ?neutron/sqlcmjsecs basediuponap-Q l proximately 7., Vkwl/ liter ofsolution.

Should heavy water he} utilized'as' the moderator; the j dimensions of the, critical regionv would have-'to be -increased accordingly, and this wouldabout double the ther 's mal neutron flux ata given powerlejver. This would ne-fi cessitate, a decrease in the-quantity ofU i required to maintain a particular power output-t -,It;sho'uld be's'noted that the term water as used herein,-u'nless otherwise specifically indicated, includes both normal. water and heavy water, and that'enrichments' ofiU. other than percent are specifically contemplated.

Further, liquid materials .other than water, for'example, 1 V slurries, and :low boiling point fused salts and .organic liquids, such as, UF are specifically contemplated. The

term fiss'ionable' material, as used herein, means material which ,r'readily undergoes Lfission when; bo'mbarded-by a alsobenoted that the quantities arid proportions pointed out above are only approximate; and that the 4 calculationof the exact values depends upon the fluxdesired, the de sired operating power level, the 'si ze'of'the reactor, the amount of effective poisoning components in the solution,

and'the moderator and 'reflector -utilized.- Thus, it is ap parent that the exact physical meaning of critical regio'riwill idepend upon a number of variable 'fa'CiOiIS 'However,;.in any case this'term necessarily'implies a fuelmoderator concentration in a critical geometry 'sufilcient to sustaina fission chainreaction, i. e.,'-the effective" neutronmultiplication factor is" at least 'unityfl In thespecific embodiment being described 'the entire region 14 within the-vessel I1 is the critical region, since'the re-i action shell 17 merely functions as'a flow directing-bathe having negligibleneutroniethickiiessJ I i START-UP OPERATION In up the reactor of the present'inventionthe- I' sleeve 34 is raised to about the half-way position to' allow f a portion :of the neutrons reflected-back to enter the'f' critical regiont The vessel 11 is then evacuated througli pipe'36 by a' standard vacuum system not shown. The reactor of the" present invention is preferably operatedwithpractically 1 all air: removed. i Although: this is not essential to opei' ability, =ithas certain advantages, such: as, the over-all: internal pressure during operationwill be" reduced, the

efiiciencyt of; the condensing surfaces will-lbe increasedgand the highwater-vapor content will decrease the possibility of explosions of the oxygen-hydrogen mixtures resulting from' the radiolytic decomposition of thewater moderator.

The liquid fuel is then introduced through inlet pipe 30. As the fuel solution is introduced, various tests and "cali bration's arem'ade in accordance with'standard proce duresii' 'After th'e'level "ofthe fuel has been rai cl to the" nornial operating level-2?, i."eE, justjbelo'w the top bfth tube bundle 20, the input'of fuel =isi-stopped.'

As' the sleeve 34is raised further; the neutrons reflected backinto the critical region byth rflector will multiplication'rate is always very nearly 'one.' The fissionactivity will be maintained at thesame value.

This.arrangement results inal'rapid circula route the Thus"theefiiciency'of the fuel circplation at the dept dependent upoii the teix iperature;

ThusQth'e liquid fuel will'heaL-since thefiss'ion process jivill create heat; As'the reactor begins toheat,-the fis'sionabl liquid fuel will expand, so that its reactivity' i's reducje The efiect is to maintain such; a temperature" that th able 'fuel concentration 'shouldf be adjusted so thatthe fullvwithdrawn position of;th"sleeve -34 represents the" f desired 'maximum operating temperature, suchfas'ffo lone C. L i f3, V 1 Water isthen introduced i into heat "exchanger 22a the cooling-jacket; The err cter the water in the heat exchanger} is" to 'increase the power out'put, since the Icy it canbe seen that the power l evelbfthe-reactor is: C l -t.

trolled by theaiiioun't (if-heat removed thr ughniehm exchanger, e1; the-rate of water 3 flow which may be variedbi' -The water in the heater exchanger i sfpreferably: I ordinary filtered citywater '(not ref i erated) and preferably fiowsi-through coolant inlet andoutlet' pipes 26} and underordinary city Water'pressure; The induced, radioactivi y in the water, if it is *of sufficient purity, will be negligible and the w vater may be discarded'aft i s dg i. i

bubbles which will move upwardly because of. their buoy-- ancy. The upward" movement of these bubbles, see

Figure 3, into the tubes 20will result in the forcing of liquid 'fuelout of the top ofthesetubes. Therefore, as V the liquid fuel beats, a current'is created by "virtue ofthe'f Y rising bubbleswhich will also be aided by the natural 1 convection circulation In this manner the liquid fuel I will circulate from the reaction shelf 17 up the tubes 20 down throughltherheat exchanger izi where it' 'is"cople'd' through "channel 19 an'd back-into the -reaction"s hel j through apertures 18 where it will again be heatedby the critical reaction taking place;

liquid 1 fuel," and I dispenses with if the "complications 1 pr;

mechanical-circulating systems;- Further'more gthereactor powerule'v'el will-begunperturbed by=the ripples or the geyserelfectvtakin'g place on'theliquid fuel surface, s i'nc'e' I -.the critical Yregionjs located in a relatively remote' pla'ee withi respect to t the surface perturbations. The r bubble formediwithin the liquid fuel'will -be swept from there action shell by the circulation befo're there has'been s'uf ficient time to appreciably aifect the reactivityi This can beseen by considering the fact that a complete circulation cycle will take of the order of Sisecorids.

Thus the complicated controlrod fniechanisms, whi are required in'prior'art devices" in order to maintain K accurate control ofjthe i V V in the present'invention.- t

The bubbles, bo th1'st'eam and gas, "rts g"t hro'ughthe a tubes '20 push the =li'quidfuel npwardlvandeject it'out of the top of 'the'tube where it falls 'back'towa'r ftheout side. =Thisgey'ser action is randar'n, so'thatnot anpf me I itubes are" functioning to circulatethe fuel atthe same timeJL'IThe tubes'at the "center of the" tube 'bundlef'will" function at the greates't' rat e, sin'ceal'argepart of the bubbles inthe liquid fuel in the reactionshell' are for nearu the center whe're the'item'perature is 'theliig Ihwbuhlilss o m d at hei e s .r te ar i s t f el n s nt lu swt op eve cci y of F f e in t e u es 2 1 n ably e e tha the yeIQtSityJ 'at any other point in the system. 1 Thus, this higher velocity aids in geyser elicit;E Obviously, this ios ta in Pla in a h o th m Th i c n be seen that the number of'tubes, i. e., the to tal area' of;;;

the. tubes with respect to thc' cross sectional area ofireaction shell, are interrelated Ithasgbeen found,that if, l

the i l. j f i t-4 1 2 un e is from b t o -th to about one-half of the cross sectional area of, the reaction shell excellent efliciency results. However, it should be hoted thatthis relationship is not a requirement; since it is within the purview of this invention to'utlize a cylindrical reaction shellaving a diameter equalto the. diameter ofthetube bundle. j 1

e il d o t fthet p .of he- 20 may be directed outwardly hy a lip -(not. shown) on the. top of each tube. In manner the fuel may be moved, into the heat exchanger region 22 Where it will. be cooled and circulated downwardly into channel 19. The fuel, in channel 19, constitutes a portion ofthe critical since-the neutrons from; the surrounding reflector,'as ;well as fromthe liquidtuel within thej icritical shelhwill cause fision to take place. Thus,'as the fuel moves downwardly in channel; 19, the heating process has already begun, and upon passage through aperture 18 jenters the ho t'leg' of'ithecirculatior'i cyerew The rcactorofthe resent} invention may be operated at a large range of temperatures; eXamples of which are' shown in the chart below.

Chart Temperature,. 100 0. 180 0. 343. 0.

Liters of steam per liter of soup per second at 300 kw cm 12. 4 1. 44 Tube length cm 25 25' 25 Tube diameter; cm .8 to 1.5 .7 to 1.4 .6 to,1.2

It isapp arent from this chart that thefefficiency of" the circulation is dependent upon the operating temperature, since 7 the volume of steam produced is reduced IWith. in-

creasing temperature and this volume controls bubble" formation.; &;Eurther, sinceat the higher operating tern peraturcs 'the'pressure Withinithe vessel is.higher, the size of the bubbles will vary. with. operating temperature.

Thus after selecting theoperating-temperature, the "tube diameter and length are :determined'. A For" a reactor power level of 300 kw." and a critical region, of 25cm; height, it is :apparent from the chart-that an increase in operating temperature results ,in ;the necessity. for a smaller diameter tube .in order to maintain the'same relative, circulation rate.

GA S 'CIRCULA TION I t The gases liberated:byithegradiolytic dissociation of the water moderator and the;moderator.vapor move intov the .areaimmediatelyabove the solution surface. Baflies 28 function to prevent any liquid fuel from splashing or otherwise reaching the recombiner apparatus. The dis-'1 socia'ted gases and vapor flow into the chimney 31' Where-J they pass over a catalyst. The catalyst func'tions to re combinc the hydrogen and oxygen gases to form" water.

During this recombination, heat is liberated, whereby...

the gases are, caused to fiow up the chimney 31. The

recombinedgases and vapor fiowoyerthe top of Chlilll-J ney 31 into the "cooling and condensihg channel; The

cooling action of the w ater jacket and; the, inlet pipes.

condense the water vapor which is directedgha'ck intofthe fuel solution by bailles- Non-condensed gases pass 'into The 'recombiher unit operation is more spe :ficallydc the'ihot' leg andv continue about the convention circuit. :I

the. heat exchanger.

erator gases are circulated over therecombining catalyst and; are, condensedjwithoutithe use of circulating ma chinery. Furthermore, this; arrangement makes-'itpo'ssible'to place the recombining unit within the same vessel .as the critical region thereby, dispensing with burdensome and hazardous handling of explosivejradioactive gases I The fact that the recombination takes place proximate, to. the liquid fuel means that the shielding o'f'the reactor also functions as a shield for the gasi'ecombiner. arrangement and association of components is more fully described'in co pe'nding' application Ser. No. 500,710,

filed April 11, 1955 by R. 'P; Hammond and Harold M. Buscy, entitled Homogeneous Nuclear Reactor, the,

disclosure of which is in'cgrporated herein-by referencei COIfITROL The temperature of the liquid fuel can be accurately controlledby the "proper positioning of the sleeve34 "or the adjustment of the fissionable material content of the liquid fuel: The available reactivity may also'be con trolled'by'using a control rod, no't shown, if desired. However, the utilizationof a control rod will increase'the fuel: requirements, and is not required. The negative temperature coefiicient offreactivity plus the "absence of perturbations within the critical region 'will result in good neutron flux stability. V

Another :method'of controlling the reactivity of the preferred. embodiment'of the present invention is by the addition or removal of water from the solution. This can be-accomplishediby apparatus well known in the art. See co-pending application Sen -No. 500,710 referred to above.

One embodiment of the present invention which is specificallycontemplated is one in which there is no recombination of gases within the" reactor vessel. In this embodiment the heat-exchanger is located within the same pressureavesselras thekcritical reaction region, but-is" not within the critical geometry; i. e;-, inthe same-manner as the preferred embodiment, andixa'plurality' oftubes- :7 20 are utilized. :lHowever', the gas recombining appara-' tus or gasventi'ng apparatus 'would be in accordance with thetea'chin'gs-of the prior art, i. 'e.-, located external to the reactor :vessel. Figure 4,of'the attached drawingswhcrein the parts designated-are the same as described hereinbefore'except" that a; gas outlet36is provided in 'this embodiment so that the radiolytically decomposed moderator gas can homogeneous-reactor, i; e.;*:negative temperature: c'o-' efficientof reactivity and easeof control; are utilizedr Thus, it is apparent that the preferred embodimentiof thepresent invention provides 'asystem "in :which the rate at which the 'fuel is circulatedisdependent upon the:operatingtemperature. 'In this manner there is con'r-' plete' power control of; the nuclear reactorx- This "can be seen by considering that the rate at which tlieheat is removed by the heat exchanging-system-willcontrol" the powerleveliofthe reactor.

Eu rt her, it can be'seen .thatthe reactor of, the present invention has a reduced critical region dimension, since l the heat egtchangeghas becnIremoye'd from this-region thereby eliminating utron absorption inthisarea' by radipactiyity of the fcoolant, because 'thecoolant isinot located in'thejighest flux region. As a result, the-coolant Such an embodiment "is shown' in ,This location also .i'educes 'the requires less safety precautions because of the lower induced radioactivity and the resulting shorter decay period to tolerable levels.

It is also apparent that the reactor of the present invention may be easily removed from its operating location, since all connections are made at the top of the vessel, thereby facilitating disconnection. Furthermore, all internal components are suspended from the top plate assembly so that removal for replacement or repair may be easily accomplished.

The preferred embodiment of the present invention utilizing a liquid fuel of uranyl sulfate and normal water does not require extensive corrosion protection of the reactor vessel or component parts. However, such corrosion protection in the form of gold, silver, platinum or similar material may be required for fuels other than the preferred liquid fuel.

It is, therefore, apparent that the present invention provides a novel arrangement and association of parts which results in a nuclear reactor having a simple yet eflicient circulating system. While presently preferred embodiments of the invention have been described, it is clear that many other modifications may be made without departing from the scope of the invention. Therefore, the present invention is not limited by the foregoing description, but solely by the appended claims.

What is claimed is:

1. A homogeneous nuclear reactor comprising a vessel containing in combination a volume of liquid nuclear fuel including a fissionable material and a liquid moderator, means for attaining nuclear criticality in a region of criticality in said liquid fuel, and means including a plurality of small diameter vertically disposed tubes extending upwardly from said region of criticality to provide circulation of said liquid fuel from said region of criticality, said tubes producing a geyser effect for forcing liquid fuel out the top of said tubes when said liquid fuel is heated, said volume of liquid fuel having a level below the upper extremity of said tubes and above said critical region, and a channel for returning liquid fuel, from the top of said tubes to said region of criticality.

2. A homogeneous nuclear reactor comprising a vessel containing in combination a volume of liquid nuclear fuel including a fissionable material and a liquid moderator, means for attaining nuclear criticality in a region of criticality in said liquid fuel, and means including a plurality of small diameter vertically disposed tubes extending upwardly from said region of criticality to provide circulation of said liquid fuel from said region of criticality, said tubes having a length about equal to the height of said region of criticality and producingra geyser effect for forcing liquid fuel out the top of said tubes when said liquid fuel is heated, said volume of liquid fuel having a level below the upper extremity of said tubes and above said critical region, and a channel for returning liquid fuel from the top of said tubes to said region of criticality.

3. A homogeneous nuclear reactor comprising a vessel containing in combination a volume of liquid nuclear fuel including a fissionable material and a liquid moderator, means for attaining nuclear criticality in a region of criticality in said liquid fuel, and means including a plurality of small diameter vertically disposed tubes extending upwardly from said region of criticality to provide circulation of said liquid fuel from said region of criticality, said small diameter tubes having a length about equal to the height of said region of criticality, said tubes having a diameter the same order of magnitude as the diameter of the bubbles, formed during the heating of the liquid fuel in said region of criticality, upon reaching the upper portion of said'tubes, said tubes producing a geyser effect for forcing liquid fuel out of the top of said tubes when said liquid fuel is heated, said liquid fuel having a level below the upper extremity of said tubes and above said critical region, and a channel for returning liquid fuel from the top of said tubes to said region of criticality. 7

4. A homogeneous nuclear reactor comprising a vessel containing in combination a volume of'liquid nuclear fuel including a fissionable material and a liquid moderator, means for attaining nuclear criticality in a region of criticality in said liquid fuel, and means including a plurality of small diameter vertically disposed tubes to provide circulation of said liquid fuel in said region ofrtcriticality from said region of criticality, said tubes extending upwardly from a flow directing baflile located in said region of criticality, said tubes being located above said region of criticality, said tubes and said bafllle being spaced from the walls of said vessel thereby forming a channel for returning the liquid fuel from the top of said tubes, said tubes producing a geyser eifect for forcing liquid fuel out the top of said tubes when said liquid is heated, said volume of'liquid fuel having a level below the upper extremity of said tubes and above said critical region. i

5. A homogeneous nuclear reactor comprising a vessel containing in combination a volume of liquid nuclear fuel including a fissionable material and a liquid moderator, means for attaining nuclear criticality in a region of criticality in said liquid fuel, and means including a plu-.

rality of small diameter vertically disposed tubes to provide circulation of said liquid fuel in said region of criticality from said region of criticality, said tubes extending upwardly from a flow directing baffle located in 7 said region of criticality, said tubes being located above said region of criticality, said tubes and said baffle being spaced from the walls of said vessel, thereby forminga channel for returning the liquid fuel from the top of said tubes to said regions of criticality, said tubes producing a geyser effect for forcing liquid fuel out the top of said tubes when said liquid is heated, said volume of liquid fuel having a level below the upper extremity of said tubes and above said critical region, heat exchanger means located in said channehsaid plurality tubes having ReferencesCited in the file of this patent Proceedings of the International Conference on the Peaceful Uses of Atomic Energy, United Nations: King,

- vol. 2. (1956), pp. 377, 387 and 391; Iskenderian et 211.,

vol. 3 (1955), pp. 163-4; Harrer et 211., vol. 3 (1955), V pp. 251-2. l 

1. A HOMOGENEOUS NUCLEAR REACTOR COMPRISING A VESSEL CONTAINING IN COMBINATION A VOLUME OF LIQUID NECLEAR FLUID INCLUDING A FISSIONABLE MATERIAL AND A LIQUID MODERATOR, MEANS FOR ATTAINING NUCLEAR CRITICALITY IN A REGION OF CRITICALITY IN SAID LIQUID FUEL, AND MEANS INCLUDING A PLURALITY OF SMALL DIAMETER VERTICALLY DISPOSED TUBES EXTENDING UPWARDLY FROM SAID REGION OF CRITICALLY TO PROVIDED CIRCULATION OF SAID LIQUID FLUID FROM SAID REGION OF CRITICALITY, SAID TUBES PRODUCING A GEYSER EFFECT FOR FORCING LIQUID FUEL OUT THE TOP OF SAID TUBES WHEN SAID LIQUID FUEL IS 